We are studying catabolic mechanisms of the myocardium with particular emphasis on the lysosomal system. We have characterized the phospholipid-hydrolyzing phospholipases A of the myocardium, polymorphonuclear leukocytes and macrophages. We are investigating the participation of these and other acid-active lysosomal hydrolases in experimental myocardial ischemia, the level of which has been estimated using radioactive microspheres. Enriched particulate fractions of normal and ischemic tissue have been studied for correlations of enzymatic changes with altered blood flow. In addition, new extraction procedures have been developed to permit maximal yields of organelles from relatively small samples of myocardium. We have extended our work to include isolation and characterization of fractions enriched in sarcolemma because of the probable participation of this membrane system in the pathology of early ischemia. Ultimately, we plan to try to correlate changes in catabolic enzymes, lysosomal latency, structural lipids and membrane-bound sarcolemmal enzymes as a part of the earliest molecular events that are altered by ischemia. Model systems are being developed to study the mechanism of loss of lysosomal latency; endogenous lysosomal phospholipases A appear to participate in this process. Triton 1339-loaded lysosomes and Imferon-loaded lysosomes have proven useful in this work; we anticipate that highly pure unloaded lysosomes will prove to be most appropriate. The ultimate goal of all of the above studies will be to identify interventions (physiological, pharmacological etc.) that can retard the release of lysosomal hydrolases and the pathobiological events that occur subsequent to ischemia.